PERIODS OE TRANQUILLITY. 
403 
new islands and mountains, bj commotions propagated with 
the rapidity of an electric shock, finally by those subter- 
ranean thunders,* heard during whole months, without 
shaking the earth, in regions far distant from active 
volcanos. 
In proportion as equinoctial America shall increase in 
culture and population, and the system of volcanos of the 
central table-land of Mexico, of the Caribbee Islands, of 
Popayan, of los Pastos, and Quito, shall be more atten- 
tively observed, the connection of eruptions and of earth- 
quakes, which precede and sometimes accompany those 
eruptions, will be more generally recognized. The volcanos 
just mentioned, particularly those of the Andes, which rise 
above the enormous height of two thousand five hundred 
toises, present groat advantages for observation. The 
periods of their eruptions are singularly regular. They 
remain thirty or forty years without emitting scoriae, ashes, 
or even vapours. I could not perceive the smallest trace 
of smoke on the summit of Tunguragua or Cotopaxi. A 
gust of vapour issuing from the crater of Mount Vesuvius 
scarcely attracts the attention of the inhabitants of Naples, 
accustomed to the movements of that little volcano, which 
throws out scoria) sometimes during two or three years 
successively. Thence it becomes difficult to judge whether 
the emission of scoria) may have been more frequent at 
the time when an earthquake has been felt in the Apen- 
nines. On the ridge of the Cordilleras everything assumes 
a more decided character. An eruption of ashes, which 
lasts only a few minutes, is often followed by a calm of 
ten years. In such circumstances it is easy to mark the 
periods, and to observe the coincidence of phenomena. 
If, as there appears to be little reason to doubt, that the 
destruction of Cumana in 1707, and of Caracas in 1812, indi- 
* In the town of Guanaxuato, in Mexico, these thunders lasted from 
the 9th of January till the 12th of February, 1784. Guanaxuato is 
situated forty leagues north of the volcano of Jorullo, and sixty leagues 
north west of the volcano of Popocatepetl. In places nearer these two 
volcanos, three leagues distant from Guanaxuato, the subterranean 
thunders were not heard. The noise was circumscribed within a very 
narrow space, in the region of a primitive schist, which approaches a 
transition-schist, containing the richest silver, mines of the kuown world, 
and on which rest trap-porphyries, slates, and diabasis (grtlnstein.) 
